A wide variety of health ailments involving cardiac arrhythmias can be effectively treated with implantable cardiac stimulation devices. The range of arrhythmias includes various bradycardia conditions, which can be treated with cardiac pacing and tachycardia conditions, which can be treated with anti-tachycardia pacers and/or implantable cardioverter/defibrillators as appropriate to the patient's condition. The implantable devices used range in complexity and modes of therapy delivery, such as the particular chambers of the heart which receive therapeutic stimulation, depending on clinical evaluations of the individual needs of the patient. Thus, an implantable cardiac stimulation device and corresponding implantable sensing/stimulation lead(s) are configured and programmed for the individual needs of each patient and their arrhythmic condition.
Cardiac arrhythmia conditions also frequently occur coincident with a congestive heart failure (CHF) condition. CHF refers broadly to a variety of health ailments characterized by a reduction in the mechanical ability of the heart to pump an appropriate supply of blood. CHF can encompass an enlargement of the heart muscle, a degradation of the contractile properties of the heart, and/or a reduction in the synchrony in the cardiac contractions. CHF can also correspond to damage to or deterioration of heart valves and other structural conditions which reduce the cardiac output.
Multi-chamber pacing can offer significant benefits to certain arrhythmic patients and frequently such patients also suffer from some degree of CHF. Bi-ventricular pacing is one particular variation of multi-chamber pacing that refers to pacing both the right and left ventricles as indicated. By providing paced control of both ventricles, bi-ventricular pacing can help restore synchrony between the ventricles and increase the overall pumping efficiency of the heart. While this treatment can be quite effective for certain patients, including many CHF patients, some patients do not respond well to bi-ventricular pacing.
Multi-chamber pacing is one of the more complicated therapies available via implantable cardiac stimulation devices. In the particular example of bi-ventricular pacing, as the left ventricle (LV) provides the most energetic contractions of the heart chambers and placing foreign objects inside the LV presents serious risks, implanting stimulation leads into effective contact with the left ventricle is a challenging procedure both for the designers of the implantable device and the physician performing the implantation. Thus, bi-ventricular pacing, while offering significant benefits to certain patients, is also relatively expensive to implement and involves a more complicated and potentially more risky implantation procedure than other implantable device configurations. As many potential implantees are covered by either private or governmental health insurance, it will be appreciated that this more complex and expensive therapy is often reserved for patients for whom a clear potential benefit can be demonstrated.
Thus, it will be appreciated that being able to readily identify and characterize either the onset of a condition which is likely responsive to multi-chamber pacing as well as the ongoing severity of the condition can provide a valuable diagnostic tool to a clinician to provide more effective therapy. A variety of examinations and observations are known which can be utilized by a clinician to evaluate the existence or progression of a CHF condition and to identify indications for multi-chamber devices. A physical examination and interview of the patient can reveal, for example, edema and/or weight gain caused by fluid accumulation, which is a frequent symptom of CHF. Shortness of breath is also a common symptom of CHF and an interview of the patient and examination can reveal the severity of and conditions under which the shortness of breath occurs. An examination can also reveal a third heart sound, frequently referred to as S3, as well as a sound of fluid in the lungs during inspiration (rales), either of which are common symptoms of CHF. A clinician may also observe enlargement of the jugular vein in the neck region (jugular venous distention), enlargement of the liver (hepatomegaly), and this may be coupled with a hepatojugular reflex wherein an enlarged liver which is subjected to manual pressure forces more blood into the jugular veins, causing them to become even more enlarged.
Several diagnostic tests are also useful in diagnosing CHF, including chest x-rays which can reveal pulmonary edema, an enlarged heart, and pleural effusion. Electrocardiograms (EKG/ECGs) are also useful for their ability to detect the presence of a heart attack, cardiac ischemia, abnormal heart rhythms, and/or an enlarged heart. Echocardiograms are another useful diagnostic tool which can determine the amount of blood ejected from the heart with each heartbeat, and more particularly, the proportion of blood ejected which is typically referred to as the ejection fraction. Ejection fraction is frequently depressed in likely responders to multi-chamber pacing. Echocardiograms can also diagnose particular causes of CHF, including heart valve abnormalities, pericardial abnormalities, congenital heart disease, and/or an enlarged heart. Echocardiograms can also show if the contraction of the heart itself is abnormal, such as in wall motion abnormalities, which lead to contractile dysynchrony, another indicator for multi-chamber pacing.
While these clinical observations and diagnostic tests offer valuable information for diagnosing a patient's condition, they suffer from the disadvantage of requiring the direct intervention of a highly trained clinician. The aforementioned patient observations require the training and judgment of a skilled clinician to accurately diagnose the patient observations. The aforementioned diagnostic tests, in addition to requiring the services of a skilled clinician, also typically require that the tests take place in a clinical setting. Diagnostic equipment, such as chest x-ray and echocardiogram machines, are large, complex, and relatively expensive pieces of equipment which are neither portable nor economical for the dedicated service of a single patient. Thus, the aforementioned observations and diagnostic tests are not suitable for frequent ongoing diagnosis of a patient's condition but rather are more suitable to serve relatively large number of patients at scheduled clinical appointments.